Fuel combustion method and reactor

ABSTRACT

The invention relates to a method for combustion of fuels of arbitrary state of aggregation, which are burnt with air, possibly with the addition of water, and a reactor therefore, which is intended to optimize the combustion method. A solid, liquid and/or gaseous fuel, possibly water and/or an oxidizing agent are introduced into a reaction chamber ( 2 ) in its axial direction under high pressure, the amount of injected pressurized air corresponding to the amount of air necessary for the complete combustion, and the introduced mixture is led to a deflection surface ( 7 ) in the interior of the reaction chamber ( 2 ), whereby it is atomized, sublimates and/or evaporates and burns explosively, before it can reach the wall or the bottom of the reaction chamber ( 2 ). The reactor ( 1 ) for this combustion method features a hyperboloidal reactor head ( 3 ), which is disposed adjacent to the outlet opening of the reaction chamber ( 2 ) and the cross-section of which widens from there, whereby the reactor ( 1 ) is shaped like a nozzle.

This applications claims the priority of international patentapplication number PCT/EP98/07175, filed Nov. 10, 1998, and of Germanpatent application number 197 49 688.1, filed Nov. 10, 1997, both ofwhich are incorporated herein by reference.

The invention is related to a method for the combustion of fuels, inwhich the fuels are burnt together with air, possibly with the additionof water and/or an oxidizing agent, and a reactor for such a combustionmethod with a reaction chamber having supply openings for the fuel, theair, possibly the water and/or an oxidizing agent and an outlet openingfor the combustion products.

An apparatus and a method for the combustion of oil with the addition ofwater are known of WO95/23942, in which oil is introduced into acombustion chamber until an oil bath has formed, which is then preheatedto a temperature between 250° C. and 350° C. Then water is sprayed ontothe surface of the hot oil bath, which results in a flame eruption withthe simultaneous supply of air into the combustion chamber. The level ofthe oil bath should not remain under a height of 3 to 4 mm duringcombustion in order to prevent an interruption of the combustion. Theapparatus used to this purpose includes in general a combustion chamberin the form of a frustrum of a pyramid or a cone with lateral supplyopenings for oil and water from corresponding reservoirs. The oil bathis electrically heated. Air enters along with the water into theinterior of the combustion chamber. The flame with a temperature of1200° C. to 2000° C. is introduced into an oven via a cylindrical tubefor heating purposes.

In this known method of combustion especially of waste oils thetemperature gradient appearing in the oil bath in the direction to thebottom has proved to be disadvantageous, because the bottom temperaturecan be lower than the evaporation temperatures of heavy fractions in thewaste oil the result of which is that the latter form a not completelyburnable oil mass at the bottom of the combustion chamber. Injecting theoil via a nozzle is not practical, because residues and highly viscouscomponents in the waste oil will lead to a clogging of the nozzles.Moreover the entire apparatus with its feeding and preheating means getsconstructively complex. Because of the remaining residues the processcontrol is hard to perform, especially when shutting down. Therefore thefacility is not suited for a continuous operation.

From GB 765 197 an apparatus for the combustion of liquid andliquefiable fuels is known, which consists of a cylindrical combustionchamber with an adjacent fire space, which is open to the top. Theliquid fuel is radially or tangentially introduced into the interior ofthe combustion chamber, and air is separately introduced tangentially,while the fuel is contacting the inner surface of the combustion chamberand is evaporated and burnt there. Temperatures appearing in the firespace are between 1500° C. and 1800° C. With incomplete combustion byreduced air supply the fuel is cracked with the aid of supplied vapour,whereby heavy oils are decomposed into lower hydrocarbons, hydrogen andcarbon monoxide.

Also in this known combustion method the way of supply is technicallydemanding, and moreover the danger exists that in certain wall regionsthe temperature is not sufficient for evaporation of heavier waste oilfractions, which then gather at the bottom of the combustion chamber andform a non-burnable residue there. Water vapour is here not provided forthe actual combustion but only for cracking of heavy oils.

In U.S. Pat. No. 4,069,005 the combustion of a water/fuel/air mixture inthe presence of a metal catalyst (nickel) is proposed, wherein in theinterior of the burner several stacked plates, which may also consist ofthe metal catalyst, can be disposed, to increase the efficiency of theresulting cracking. In the apparatus serving this purpose liquid fuelsand water are respectively dropped upon the catalyst from above, theplates having been heated to a temperature above 800° C. in a preheatingphase. The rising vapours are led along the metal catalysts, wherebyeasily burnable, gaseous hydrocarbons are generated by cracking, whichburn in the further process, whereby combustion gases of 800° C. to1000° C. are generated.

For the generation of a long flame for heating an industrial boiler inU.S. Pat. No. 3,804,579 oil and air are burnt together with watervapour, which is generated in a heat exchange coil by the flame. Herethe extended flame burns at about 730° C.

Finally from DE 39 29 759 C2 a facility for burning waste oil productsis known, in which the waste oils are mixed with a usual heating oilwith a known smaller viscosity, such that an average product withconstant viscosity is, formed, which is then preheated and injected intoa tank. On the opposite side of the tank input devices for air, waterand common neutralizing agents are provided. For injecting the oilmixture air or water vapour is used. The control facility for the mixingratio of the oils and the injection apparatus for the oil mixture withadditional supply leads for air and neutralizing agents lead to aconstructively complex facility, which is hard to control, and whichcannot work efficiently, because apart from the actual combustionproduct of waste oil considerable amounts of normal heating oil have, tobe burned additionally, which largely limits the disposal capacity. Thesimple combustion tank cannot support the combustion process.

It is an object of the present invention to provide a method for theenvironmentally friendly combustion of fuels of an arbitrary state ofaggregation, possibly with the addition of water and/or an oxidizingagent, in which the fuel is burnt without residues with a high energyefficiency. The reactor suitable for this is intended to optimize thecombustion process in continuous operation with a low constructiveeffort, and it should be as maintenance-free as possible, and it shouldbe self-cleaning.

According to the invention the solid and/or liquid and/or gaseous fuel,possibly the water and/or an oxidizing agent are introduced into areaction chamber under high pressure in axial direction by pressurizedair, the amount of injected pressurized air corresponding to the amountof air, which is necessary for the complete combustion, the introducedmixture is led to a deflection surface in the interior of the reactionchamber, whereby it is further atomized, liquid components evaporate,solid ones sublimate and the mixture burns explosively, before it canreach the wall of the bottom of the reaction chamber. The explosivecombustion process can be explained by the high degree of the surfaceincrease of the mixture introduced into the reaction chamber:

(a) the fuel supplied by pressurized air is disintegrated and atomized,when it is injected into the reaction chamber,

(b) the existing pressure is still sufficient to lead the fuel with highvelocity to a deflection surface in the interior of the reactionchamber, where an impingement and a reflection with a furtherdistribution and atomization are caused.

Additional water injected with pressurized air is atomized intodroplets, when entering the reaction chamber, the droplets changing intowater vapour and being distributed into all directions in the interiorspace of the reaction chamber by the deflection surface. The expansioncaused by the sudden evaporation supports a mixing of the fuels with thepresent pressurized air and the water vapour, which leads to anefficient combustion, especially of hardly burnable fuel components.This way a precipitation of fuel at the inner wall and a concentrationof residues at the bottom can be more efficiently abided, so that thereactor cleans itself.

The pressurized air flow can be injected at 2 to 10 bar, preferably at 3to 5 bar into the reaction chamber. At these pressures the combinationof the atomization at the exit from the supply lead with the one causedby the impact onto the deflection surface in the interior space of thereaction chamber is especially efficient.

The fuels, the water and/or the oxidizing agent are respectivelyintroduced separately or as a mixture via one or several Venturi tubesinto the pressurized air flow. Gaseous fuel can thereby be individuallyintroduced into the reaction chamber. This way of supply allows for agood dosibility with a low constructive effort and simultaneouslyenhances the atomizing effect at the entrance into the reaction chamber.The injection into the reaction chamber is accomplished by a normal tubeof a small diameter without a nozzle top, whereby a clogging of thenozzle at the time of combustion of waste oils by non-burnable residuesor highly viscous components is prevented. The constructive effort islowered furthermore by the use of uniform Venturi tubes for the supplyof the fuels and the water.

It is favorable to keep the temperature inside the reaction chamberhomogeneous to the axis of the reaction chamber by heat conductingreactor walls. When by the deflection surface a symmetric distributionof the mixture inside, the reaction chamber is caused, a more uniformcombustion can be achieved at a symmetric temperature distribution.

At a predetermined geometry of the reaction chamber the inflowvelocities into the reaction chamber of the mixture to be burnt can beadjusted, so that the resulting combustion flame leaves the reactionchamber at least with the velocity of sound and the resulting heatenergy is transported to the outside for further use. This can befurther improved by suitable reactor geometries as described below.

The ignition of the mixture in the reaction chamber is preferablyperformed by a starter flame or by a generated spark. It can beadvantageous to preheat the fuels, the water or the air by the wasteheat generated in the combustion, before they are introduced into thereaction chamber. Especially heavy oil becomes easier transportable bythe decrease in velocity achieved hereby. The fluid dynamics of thecombustion process can be influenced by inserts, that can be introducedinto the inner space of the reaction chamber.

It is advantageous to additionally crack the fuel at the time ofcombustion, wherein as catalyst e.g. a nickel containing material can beused.

The reactor according to the invention has a hyperboloid reactor headswhich is adjacent to the outlet opening of the reaction chamber and thecross section of which increases from there. The combustion flame burnsat this reactor head. The nozzle like geometry of the reactor therebycauses an acceleration of the combustion gases with the formation of acorresponding vacuum in the outlet region of the reaction chamber, whichleads to a further acceleration of the substances to be burnt in theinterior of the reaction chamber in the direction of the outlet opening,which positively influences the combustion and the self-cleaning of thereactor.

The nozzle effect can be improved by a tapering of the reaction chamberat least in its upper part in the direction of the outlet opening,whereby the tapering part can be provided specially as a frustrum of apyramid or a cone. On the other hand the entire reaction chamber canhave a hyperboloid shape, so that it tapers in the direction of theoutlet opening.

With the nozzle-shaped reactor geometry it is favorable to embed thesupply openings for the fuels (and the water) into the bottom of thereaction chamber, so that these are directed parallel to the axis of thereaction chamber. Hereby the axis of the reaction chamber is determinedas the preferred flow direction, in which for the better distribution ofthe mixture to be burnt, a deflection surface can be disposed, by whichthe mixture is first deflected from the axis of the reaction chamber andis subsequently directed again to this axis by the mentioned nozzleeffect. Moreover, the effusion from the supply openings is favored bythe pressure conditions.

A cone, the tip of which is directed against the flow direction of thefuel or a pyramid of a fire resistant material, which is directed in thesame way, being disposed in the interior of the reaction chamber alongits axis, can be used as deflection surface for achieving a homogeneousdistribution. The combustion process can thereby be optimized bysymmetric distribution in the cross-section of the reaction chamber ofphysical quantities such as pressure, flow velocity, turbulence andtemperature.

If the fuel is intended to be additionally cracked, it is advantageousto provide a metal catalyst, specially a nickel-containing one, e.g. inthe interior walls of the reaction chamber in fire-resistant inserts inthe interior of the reaction chamber or even in the deflection surface.A high efficiency of the catalytic cracking can be achieved by a scaledor porous metal catalyst with a large surface.

The reactor can uniformly be fabricated of a material like stainlesssteel, but it can also, at least partially, be fabricated of a speciallyheat-resistant and mechanically robust alloy like a Ni—Mo—Cr—Co alloy(“Nimonic”). Moreover, the reactor can be surrounded by an outerinsulation of ceramics fibres or fibreglass to reduce the amount ofradiated heat and to maintain the temperature in the reaction chamberabove 1000° C.

The invention will subsequently be discussed in greater details in anembodiment referring to the figures.

FIG. 1 is a squint side view from below of a reactor according to theinvention,

FIG. 2 is a squint transparent view from above of the reactor, and

FIG. 3 is a transparent side view of the reactor.

The figures show the reactor 1 according to the invention with areaction chamber 2, with the reactor head 3 adjacent to the outletopening 4. Supply leads 5 and 6 are embedded in the centre of the bottomof the reactor 1 in coaxial direction. As deflection surface a cone 7,the tip of which is oriented in the direction of the supply leads 5 and6 is disposed along the axis in the interior of the reaction chamber 2in this example.

The upper part of the reaction chamber 2 in this example tapershyperboloidally in the direction of the outlet opening 4 and continuesfrom there hyperboloidally in the reactor head 3. This geometry causes anozzle effect, by which flowing gases are sucked out of the interior ofthe reaction chamber 2 by the vacuum in the area of the outlet openingand the reactor head, whereby the supply pressure in the supply leads 5and 6 can be additionally reduced. At the same time this enables aself-cleaning of the reactor, because non-burnable particles andresidues are sucked by the suction effect out of the interior of thereactor. Such residues can be deposited by filtering the combustiongases.

In this embodiment the reactor has a volume of about 15 litres and isfabricated of stainless steel. It is favorable to fabricate it of a moretemperature-resistant and mechanically more solid material such as aNimonic alloy, which has the following composition: C=0.057; Si=0.18;Mn=0.36; S=0.002; Al=0.47; Co=19.3; Cr=19.7; Cu=0.03; Fe=0.55; Mo=5.74;Ti=2.1; Ti+Al=2.59 (in weight percent), ppm amounts of Ag, B, Bi and Pb,balance nickel. The elements contained therein at the same time cause acatalytic cracking of hydrocarbons. The reactor can be fabricated ofthis material with wall thicknesses of 3 to 4 mm, which measure 5 to 7mm with stainless steel. An outer insulation of the reactor 1 of amaterial of ceramics fibres or fibreglass, which decreases the heatradiation and thus increases the temperature in the interior of thereactor is favorable.

By the supply leads 5, which are formed by Venturi tubes with a diameterof 3 to 7 mm liquid fuel, namely waste oil and heavy oils of differentcompositions and solid fuel, especially dried olive bagasse and sewagesludges, is sucked by pressurized air of respective (not shown)reservoirs and transported into the interior of the reaction chamber 2with pressures of 3 to 5 bar. At the exit of the supply leads 5 the fuelflow disintegrates, and the fuel impinges onto the deflection surface 7with high velocity, from which the fuel is symmetrically distributedinto the cross-section of the reaction chamber. Water injected through asupply lead 5 is atomized and evaporates when exiting into the reactionchamber 2, and the water vapour is also symmetrically distributed in thereaction chamber 2. By the supply lead 6, in which the supply leads 5are disposed, additional pressurized air can be fed on demand, in orderto provide the amount of air, which is required for the completecombustion.

About 30 to 40 l/h water and 70 to 80 l/h waste oil are introduced intothe reaction chamber 2. Solid fuels like dried biomass are supplied at110 to 130 l/h. If liquid and solid fuels are also to be introduced thesupplied amounts have to be decreased correspondingly. The power of theburner is nearly 1 MW_(t). The toxic emissions are low to negligible.

The control of the combustion process is performed by measuring thetemperature, the amount and the chemical composition of the combustiongases. Accordingly the amounts of the supplied water, air and fuel arecontrolled.

The illustrated structure of the reactor results in a symmetricdistribution of the physical quantities of the combustion processrotationally symmetric with respect to axis points of the reactionchamber 2. In a cross section of the reaction chamber 2 the values ofthe temperature, pressure, and flow velocity of the gases are almostconstant. The temperatures increase from the bottom of the reactionchamber 2 in the direction of the outlet opening 4, wherein a flatteningof the temperature gradients is caused by the heat conductive reactorwalls in continuous operation.

The fluid dynamic of the combustion process can be adjusted at a changeof the reactor geometry and the position and geometry of the deflectionsurface.

The fuels are completely burnt in the reactor. Possibly not burnableresidues are transported by the suction effect out of the interior ofthe reactor and can be collected with a filter. The nozzle effect of thereactor 1 can be adjusted together with the supply velocity, so that thecombustion gases leave the reactor head 3 with the velocity of sound ata temperature of about 1200 to 1500° C.

Different industrial applications of the reactor and combustion methodof the invention are favorable. For example, with the hot combustiongases a fluid bed can be operated, in which sand is penetrated by hotgas. Such fluid beds are usually used to clean objects (for example, ofvarnish residues). This use is also favorable for the disposal ofspecial waste. Biomass can be subjected to a pyrolysis process on thefluid bed by intentional lack of air, whereby solid and gaseous fuels,which can directly be supplied to the method of the invention, areobtained. Moreover, the generated combustion gases can be directly usedfor current generation in a combustion motor. Finally the combustionmethod of the invention can be used for the combined generation of heatand electric current, i.e. for the operation of vapour turbines and alsoof gas turbines.

The invention permits an environmentally friendly combustion of hard todispose waste products like waste oils of different composition, sewagesludges, olive bagasse, mineral carbon and other burnable wasteproducts.

What is claimed is:
 1. A method for the combustion of fuel in a reactionchamber having an axis, wherein the reaction chamber is capable ofburning liquid, solid and gaseous fuels, the fuel is introduced into thereaction chamber in an axial direction by means of pressurized air andburned, said method comprising the steps of: (a) providing a fuel; (b)generating a mixture of the fuel and the pressurized air, wherein theamount of pressurized air corresponds to the amount of air required forcomplete combustion; and (c) leading the mixture to a tapered deflectionsurface disposed entirely within an interior of the reaction chamber,whereby the mixture is distributed, so that any liquid components arefurther atomized and evaporated and any solid components are furtheratomized and sublimated and the fuel mixture starts to burn explosively,before it can reach the wall or the bottom of the reaction chamber, witha combustion flame occurring at a reactor head coupled with the reactionchamber and having a hyperboloidal shape.
 2. The method of claim 1,wherein the pressurized air flow is injected into the reaction chamberat a pressure of about 2 to 10 bar.
 3. The method of claim 1, whereinthe inflow velocities into the reaction chamber are adjusted so that thecombustion flame leaves the reaction chamber at least with the velocityof sound at a predetermined geometry of the reaction chamber.
 4. Themethod of claim 1 wherein the fuel is burned with water present.
 5. Themethod of claim 1, wherein an oxidizing agent is used with the fuel. 6.The method of claim 1, wherein a hydrocarbons containing fluid iscatalytically cracked in the combustion.
 7. A reactor capable ofcombusting liquid, solid, and gaseous fuels, wherein fuels are burnedtogether with air, said reactor comprising: a reaction chamber withsupply openings for the fuel and the air; an outlet opening for thecombustion products; a hyperboloidal reactor head disposed adjacent tothe outlet opening of the reaction chamber; and a tapered deflectionsurface disposed entirely within an interior of the reaction chamber fordistributing a fuel.
 8. The reactor of claim 7, wherein the reactionchamber tapers at least at the upper part in the direction of the outletopening.
 9. The reactor of claim 8, wherein the tapered part of thereaction chamber is formed as a frustum of a pyramid or a cone.
 10. Thereactor of claim 8, wherein the reaction chamber is formedhyperboloidially.
 11. The reactor of claim 7, wherein the openings ofthe supply leads are embedded in the bottom of the reaction chamber andare directed parallel to the axis of the reaction chamber.
 12. Thereactor of claim 7, wherein the deflection surface is formed by a coneor pyramid, the tip of which points in the direction of the supplyopenings.